Protractors and similar devices have long been used to locate the center of a circle, or a circular structure such as a tube or pipe. But such devices lack means to project that center from one surface to another, which creates some problems in the building trades.
One such problem, is where a plumbing pipe emerges from a hole in the ceiling and must extend downwardly therefrom through a space (the height of the room) and then pass through a corresponding hole in the floor beneath. It is desirable that the hole in the floor be the same size as the hole in the ceiling and directly beneath it. In the past this has generally been attempted by measuring the distance from adjacent walls. This is very imprecise because walls rarely plumb true and the multiple measurements inevitably result in some degree of error. So the hole in the floor ends up being considerably larger than the hole in the ceiling, and having undesirably large gaps between the hole and the pipe it is intended to accommodate.
The same problem arises, when a pipe emerges horizontally from a hole in one wall and must extend through a space (the length of the room) to pass through a corresponding hole in an adjacent wall.
It is, accordingly an object of the present invention to provide a device for determining the center of a pipe, which can also precisely project that center to a distant surface.
It is a further object of the invention to provide means for temporarily attaching such a device to the end of a pipe during the period of measurement.
It is a further object of the invention to provide the aforesaid device of a material which is rigid, but sufficiently flexible to fit around the curvature of a pipe.